The invention relates to a gas conduit pipe for a gas bag module.
A gas conduit pipe usually has at least one outflow opening arranged in a peripheral wall, the edge of the outflow opening being defined by an upstream section and a downstream section of the peripheral wall, which both project into the interior of the pipe.
Such gas conduit pipes, also known as gas lances, serve to direct the gas necessary for inflating a gas bag from a gas generator to the gas bag. The main purpose of use of such gas lances is in side gas bags which have a large area. Here, it is particularly important to fill the gas bag as uniformly as possible from several places, so that the gas bag can unfold quickly. Through the construction of the outflow openings provided in the peripheral wall of the gas lance, the flow of the gas into the gas bag can be increased and thus the inflation time of the gas bag can be shortened.
A construction of the outflow openings by which this can be achieved are what are known as scoop gills (e.g. DE 298 04 004). Here, a portion of the peripheral wall is pressed into the interior of the gas conduit pipe, so that a guide surface is formed for the gas. A disadvantage in this construction is that care must be taken that the gas is highly particle-free, because any particles introduced into the gas lance can be drawn into the gas bag together with the gas stream.
Another embodiment of the outflow openings, which is not so susceptible to the intake of particles into the gas bag, makes provision that the entire edge of the outflow opening is bent into the interior of the pipe. Particles in the gas are largely held back at the projecting wall. Here, of course, the through-flow through the individual outflow openings is distinctly less than with the use of scoop gills, so that means must be provided for the production of a counter pressure in the gas lance, in order to ensure a sufficiently high through-flow.
The invention provides a gas conduit pipe which offers a high through-flow into the gas bag with a low susceptibility to the intake of particles.
According to the invention, a gas conduit pipe for a gas bag module comprises a gas inlet end defining a direction of gas flow, a peripheral wall limiting an interior of the pipe, at least one outflow opening arranged in the peripheral wall of the pipe. An edge of the outflow opening is defined by an upstream section and a downstream section of the peripheral wall. The upstream and downstream sections project both into the interior of the pipe with the downstream section projecting further into the interior of the pipe than the upstream section. This construction of the outflow opening combines the advantages of the scoop gills with the raised-up edge of the outflow opening. The upright upstream section of the peripheral wall, i.e. the section arranged closer to the gas inlet end, prevents an intake of particles into the gas bag, whilst the downstream section, projecting over the upstream section, forms a guide surface for the gas stream in the manner of a scoop gill, and thus increases the gas through-flow into the gas bag.
Particles in the gas are either held back completely in the gas lance, or at least their kinetic energy is reduced to such an extent that they can not damage the gas bag.
Preferably, the downstream section in a longitudinal sectional view of the gas conduit pipe is a concave indentation, when viewed from the exterior, similar to the construction of a scoop gill.
In a preferred embodiment of the invention, the two sections are designed so as to be cohesive, so that the entire edge of the outflow opening projects from the surface of the peripheral wall into the interior of the pipe.
Preferably, the outflow opening is produced in that the peripheral wall is punched to form the two sections and the outflow opening. This can take place advantageously in a simple and quick manner through the use of a tool die, the front region of the tool die being constructed according to the desired shape of the outflow opening. The most favorable shape of the outflow opening or of the tool die can advantageously be determined quickly and at a favorable cost through a simulation. In this way, the gas lance can be coordinated quickly, simply and at a favorable cost to the requirements needed for the respective use. The sections preferably run in a half ring shape and continue into each other in a plane lying at right angles to the direction of gas flow. The half closer to the inflow opening into the pipe is the upstream section; the other half is the downstream section.